Use the new relative::LockTime module

Implement `check_older` using the new `relative::LockTime` API.

This code seems upside down, I'm not sure I have the naming correct,
i.e., I don't know which (`self` or arg) is doing the satisfying and
which is satisfied?

I believe the `<=` are going the correct direction, its the naming and
which sequence value to call the 'lock' that I'm struggling with.

src/miniscript/satisfy.rs

@@ -125,21 +125,12 @@ impl<Pk: MiniscriptKey + ToPublicKey> Satisfier<Pk> for Sequence {
             return false;
         }
 
-        // We need a relative lock time type in rust-bitcoin to clean this up.
-
-        /* If nSequence encodes a relative lock-time, this mask is
-         * applied to extract that lock-time from the sequence field. */
-        const SEQUENCE_LOCKTIME_MASK: u32 = 0x0000ffff;
-        const SEQUENCE_LOCKTIME_TYPE_FLAG: u32 = 0x00400000;
-
-        let mask = SEQUENCE_LOCKTIME_MASK | SEQUENCE_LOCKTIME_TYPE_FLAG;
-        let masked_n = n.to_consensus_u32() & mask;
-        let masked_seq = self.to_consensus_u32() & mask;
-        if masked_n < SEQUENCE_LOCKTIME_TYPE_FLAG && masked_seq >= SEQUENCE_LOCKTIME_TYPE_FLAG {
-            false
-        } else {
-            masked_n <= masked_seq
-        }
+        let lock = match n.to_relative_lock_time() {
+            Some(lock) => lock,
+            None => return false,
+        };
+
+        lock.is_satisfied_by(self)
     }
 }